1. Field
The present disclosure relates generally to a switch driving circuit and power factor correction circuit having the same, and more particularly, to a technology to provide a negative offset using Zener diodes to prevent malfunctions in driving a switch.
2. Description of Related Art
The power factor of an Alternate Current (AC) electrical power system is defined as the ratio of the real power flowing to the load to the apparent power.
This is also referred to as PF. For instance, a power factor of an AC power system having sinusoidal current and voltage waveforms is equal to the cosine of a phase angle between the current and voltage waveforms. For power calculation of a Direct Current (DC) circuit, the power is simply given by a product of current and voltage, but for power calculation of AC power, the power has to be obtained by multiplying effective values of the voltage and current by a coefficient, cosθ except for an instance where the current and voltage are in phase. A power factor of an AC power system having non-sinusoidal current or voltage waveform includes several factors, including a displacement factor related to the phase angle and a distortion factor related to the non-sinusoidal waveform.
In general, the real power (e.g., in watts) may be defined as the power that is actually used to do work; the reactive power may be defined as the power required to produce a magnetic field (e.g., consumed power) to do actual work; and the apparent power may be defined as a total power required to produce desired real power. The power factor of an AC power system may vary in the range from 0 to 1, and when the power factor is 1, it represents a pure resistive circuit without reactive power loss. When the power factor of an AC power system is not equal to 1, a current waveform may not follow the voltage waveform, thereby potentially causing power loss as well as occurrence of harmonics that pass the AC power system, which interferes with other devices. It is rare for the load that is connected to a power source to only have pure resistance components, but the load often has a capacitive or inductive components, which cause reactive power loss. Especially, in case of converting AC power to DC power for use, a smoothing capacitor is used to reduce the AC components, which may cause the power factor to be reduced. To reduce the reactive power loss, many types of power factor enhancement circuits that make the input voltage and current almost be in phase are used, and especially in an apparatus that converts AC power to a DC voltage for use, a power factor enhancement scheme with a boost converter is often used.
Accordingly, the power factor of an AC power system may increase by means of a power factor correction circuit (or PFC circuit).
The PFC circuit includes a bridgeless PFC circuit, a semi-bridgeless PFC circuit, a totem-pole bridgeless PFC circuit, etc.